Stationary diffuser

Abstract

A method and apparatus for effecting washing, bleaching, or thickening, etcetera of paper pulp or the like utilizes stationary screens, yet provides efficient treatment without significant screen clogging. Pulp introduced into the bottom of a cylindrical upright vessel is caused to flow in particular radial segments and channels. Introduction of pulp into all channels of a particular radial segment, extraction of withdrawn liquid from the radial segments, removal of treated pulp from the top of the vessel, and the introduction of treating liquid between the stationary screens, are coordinated so that uniform treatment of the upwardly flowing pulp results.

What is claimed is: 
     
       1. Apparatus for treating a suspension comprising: an upright cylindrical vessel; a central shaft mounted for rotation within said cylindrical vessel about the axis of said cylindrical vessel; a plurality of annular stationary screens disposed within said vessel and spaced from each other and from said central shaft; a plurality of radially extending extraction arms physically and hydraulically connected to said stationary annular screens, said extraction arms partitioning said vessel into a plurality of radial segments of substantially the same cross-sectional area, and said screens partitioning each radial segment into a plurality of vertically extending channels; and a suspension inlet means mounted below said extraction arms and screens and operatively connected to said shaft, said inlet means comprising means for introducing suspension into a bottom portion of said vessel with a cross-sectional area substantially the same size and shape as one of said radial segments. 
     
     
       2. Apparatus as recited in claim 1 further comprising a plurality of fluid introducing structures extending axially in said vessel, each radially spaced from said stationary screens; and means for interconnecting said fluid introducing structures to said central shaft. 
     
     
       3. Apparatus as recited in claim 2 wherein said treatment-liquid introducing structures comprise a plurality of rotatable nozzle assemblies each radially disposed between a pair of said screens for introducing treatment fluid into the suspension between said screens, each nozzle assembly comprising surface means for providing that at any point in the nozzle assembly rotation cycle the volume of treatment fluid plus nozzle assembly volume is substantially a constant. 
     
     
       4. Apparatus as recited in claim 3 wherein each said nozzle assembly comprises an axially-extending fluid introducing portion, and wherein said surface means comprises a substantially annular wall structure substantially parallel to the walls of said cylindrical vessel, and having an increasing cross-sectional area from a point immediately following said fluid introducing structre in the direction of rotation of said nozzle assembly to a point of connection to said fluiu introducing portion. 
     
     
       5. Apparatus as recited in claim 4 wherein said wall means includes exterior surfaces formed of a material having low-friction properties comparable to those of polytetrafluoroethylene. 
     
     
       6. Apparatus as recited in claim 5 wherein said wall means exterior surfaces have a plurality of circumstantial ribs thereon. 
     
     
       7. Apparatus as recited in claim 1 further comprising treated suspension removing means located adjacent to the top of said vessel, above said stationary screens, for simultaneously removing all of the suspension along a radius of said vessel, and means for connecting said suspension removing means to said central shaft for rotation therewith. 
     
     
       8. Apparatus as recited in claim 7 wherein said suspension removing means comprises a screw conveyor assembly including a screw rotatable about an axis substantially aligned with a radius of said vessel. 
     
     
       9. Apparatus as recited in claim 7 further comprising means for equalizing the upward flow rate of suspension in each channel. 
     
     
       10. Apparatus as recited in claim 9 wherein said channel suspension flow equalizing means comprises a plate having a shape corresponding to that of one or more radial segments; a plurality of pressure sensors associated with said plate; means for mounting said plate above said screens for rotation with said shaft and for pivotal movement about a horizontal axis; and force supplying means responsive to said pressure sensors for applying a force to said plate to maintain it in a particular pivoted position about said horizontal axis. 
     
     
       11. Apparatus as recited in claim 7 further comprising means for equalizing the upward flow rate of suspension in each channel. 
     
     
       12. Apparatus as recited in claim 11 wherein said channel suspension flow equalizing means comprises a plate having a shape corresponding to that of one or more radial segments; a plurality of pressure sensors associated with said plate; means for mounting said plate above said screens for rotation with said shaft and for pivotal movement about a horizontal axis; and force supplying means responsive to said pressure sensors for applying a force to said plate to maintain it in a particular pivoted position about said horizontal axis. 
     
     
       13. Apparatus as recited in claim 1 wherein each of said stationary screen structures comprises at least one screen surface having an interior supporting structure extending substantially parallel to the axis of rotation of said shaft; and means for mounting each said screen surface with respect to said supporting structure so that a top portion of said screen surface is closer to said supporting structure than a bottom portion of said screen surface, providing an increased cross-sectional area of flow as suspension moves upwardly in said vessel. 
     
     
       14. Apparatus as recited in claim 13 wherein each of said screen surfaces includes a plurality of liquid passages formed therein, each of said passages extending at a downward angle from the exterior of said screen surface toward said supporting structure. 
     
     
       15. Apparatus as recited in claim 1 wherein each screen segment of each of said screen structures in a particular radial segment is hydraulically connected to the same extraction arm, and only a single extraction arm; and further comprising extraction valve means for controlling the flow of liquid from each extraction arm. 
     
     
       16. Apparatus as recited in claim 15 further comprising back-wash valve means for supplying back-wash liquid to each of said extraction arms, in turn, when the extraction of liquid therefrom is temporarily stopped. 
     
     
       17. Apparatus as recited in claim 16 wherein said extraction and back-wash valve means comprise a common valve structure for controlling extraction from said extraction arms and supplying back-wash liquid thereto, said valve means comprising: a hollow housing having a plurality of radially extending fluid connections in fluid communication with the interior thereof, one fluid connection being provided for each extraction arm; a single back-wash liquid introducing conduit; a shaft mounted centrally of said housing for rotation with respect thereto, said back-wash conduit axially spaced from said extraction fluid connections; a valve member mounted on said shaft for rotation therewith, said valve member comprising a first portion in operative associated with said extraction fluid connections, and a second axially spaced portion in operative association with said back-wash liquid introducing conduit; and an extraction liquid outlet in fluid communication with the interior of said housing on the opposite side of said valve member as said back-wash liquid introducing connection. 
     
     
       18. Apparatus for treating a suspension comprising: an upright cylindrical vessel; a central shaft mounted for rotation within said cylindrical vessel about the axis of said cylindrical vessel; a plurality of annular stationary screens disposed within said vessel and spaced from each other and from said central shaft; a plurality of radially extending extraction arms physically and hydraulically connected to said stationary annular screens, aaid extraction arms partitioning said vessel into a plurality of radial segments of substantially the same cross-sectional area, and said screens partitioning each radial segment into a plurality of vertically extending channels; treated suspension removing means located adjacent to the top of said vessel, above said stationary screens, for simultaneously removing all of the suspension along a radius of said vessel; and means for connecting said suspension removing means to said central shaft for rotation therewith. 
     
     
       19. Apparatus as recited in claim 18 wherein said suspension removing means comprises a screw conveyor assembly including a screw rotatable about an axis substantially aligned with a radius of said vessel, and a blade-trough assembly following said screw in the direction of rotation of said removing means. 
     
     
       20. Apparatus for treating a suspension comprising: an upright cylindrical vessel a central shaft mounted for rotation within said cylindrical vessel about the axis of said cylindrical vessel; a plurality of annular stationary screens disposed within said vessel and spaced from each other and from said central shaft; a plurality of radially extending extraction arms physically and hydraulically connected to said stationary annular screens, said extraction arms partitioning said vessel into a plurality of radial segments of substantially the same cross-sectional area, and said screens partitioning each radial segment into a plurality of vertically extending channels; wherein each of said stationary screen structures comprises at least one screen surface and an interior supporting structure extending substantially parallel to the axis of rotation of said shaft; and means for mounting each said screen surface with respect to said supporting structures so that a top portion of said screen surface is closer to its respective supporting structure than a bottom portion of said screen surface, providing an increased cross-sectional area of flow as suspension moves upwardly in said vessel. 
     
     
       21. Apparatus as recited in claim 20 wherein each of said screen surfaces includes a plurality of liquid passages formed therein, each of said passages extending at a downward angle from the exterior of said screen surface toward said supporting structure. 
     
     
       22. Apparatus for treating a suspension comprising: an upright cylindrical vessel a central shaft mounted for rotation within said cylindrical vessel about the axis of said cylindrical vessel; a plurality of annular stationary screens disposed within said vessel and spaced from each other and from said central shaft; a plurality of radially extending extraction arms physically and hydraulically connected to said stationary annular screens, said extraction arms partitioning said vessel into a plurality of radial segments of substantially the same cross-sectional area, and said screens partitioning each radial segment into a plurality of vertically extending channels; and wherein each screen segment of each of said screen structures in a particular radial segment is hydraulically connected to the same extraction arm, and only a single extraction arm; and further comprising a plurality of extraction conduits, one extending from each of said extraction arms; and extraction valve means for controlling the flow of liquid from each extraction arm. 
     
     
       23. Apparatus as recited in claim 22 further comprising back-wash valve means for supplying back-wash liquid to each of said extraction arms, in turn, when the extraction of liquid therefrom is temporarily stopped. 
     
     
       24. Apparatus as recited in claim 23 wherein said extraction and back-wash valve means comprise a common valve structure for controlling extraction from said extraction arms and supplying back-wash liquid thereto, said valve means comprising: a hollow housing having a plurality of radially extending fluid connections in fluid communication with the interior thereof, one fluid connection being provided for each extraction arm; a single back-wash liquid introducing conduit; a shaft mounted centrally of said housing of rotation with respect thereto; said back-wash conduit axially spaced from said extraction fluid connections; a valve member mounted on said shaft for rotation therewith, said valve member comprising a first portion in operative association with said extraction fluid connections, and a second axially spaced portion in operative association with said back-wash liquid introducing conduit; and an extraction liquid outlet in fluid communication with the interior of said housing on the opposite side of said valve member as said back-wash liquid introducing connection. 
     
     
       25. Apparatus for the continuous treatment of a suspension in a cylindrical vessel comprising: a cylindrical vertical vessel; a plurality of annular stationary screens disposed in said vessel, and concentric therewith; means defining a plurality of radial segments, and a plurality of vertical channels in each radial segment, in said vessel; means for introducing suspension, adjacent the vessel bottom, to flow upwardly in the vessel in a moving suspension column into a cross-sectional area in the vessel corresponding to that of approximately one of the radial segments; means for substantially continuously withdrawing liquid from the majority of the stationary screens' area; means for terminating extraction from the screens in each radial segment approximately when the suspension is being introduced therein; and means for continuously removing from a top portion of said vessel, above the level of said screens, a portion of the entire radial extent of the suspension at the cross-sectional area of the top of the column preceding the radial segment into which the suspension is being introduced at the bottom of the column. 
     
     
       26. Apparatus as recited in claim 25 further comprising a plurality of treatment-liquid introducing structures rotatable about a central axis of said vessel, said structures comprising means for minimizing shock waves acting on said stationary screens as a result of liquid introduction by said introducing structures. 
     
     
       27. Apparatus as recited in claim 26 wherein said treatment-liquid introducing structures comprise a plurality of rotatable nozzle assemblies each radially disposed between a pair of said screens for introducing treatment fluid into the suspension between said screens, each nozzle assembly comprising surface means for providing that at any point in the nozzle assembly rotation cycle the volume of treatment fluid plus nozzle assembly volume is substantially a constant. 
     
     
       28. Apparatus as recited in cliam 27 wherein each said nozzle assembly comprises an axially-extending fluid introducing portion, and wherein said surface means comprises a substantially annular wall structure substantially parallel to the walls of said cylindrical vessel, and having an increasing cross-sectional area from a point immediately following said fluid introducing structre in the direction of rotation of said nozzle assembly to a point of connection to said fluid introducing portion. 
     
     
       29. Apparatus as recited in claim 28 wherein said wall means includes exterior surfaces formed of a material having low-friction properties comparable to those of polytetrafluoroethylene. 
     
     
       30. Apparatus as recited in claim 29 wherein said wall means exterior surfaces have a plurality of circumstantial ribs thereon. 
     
     
       31. Apparatus as recited in claims 25 or 26 further comprising means for controlling the ratio of the upward flow of suspension in each of the vertical channels so that the flow in each channel is substantially the same as the flow in the other channels.